For a disk driving device driving an information recording medium (hereinbelow called simply a disk) formed in a disk shape, various improvements and contrivances have been proposed in order to deal with trials to increase the recording density and to reduce the size and the weight. In one of them a turn table is mounted on a spindle shaft by inserting the latter in the former and recording/reproduction is effected by chucking a disk through a driving pin protruding from the disk mounting surface of the turn table and a chucking magnet to drive it so as to rotate.
FIG. 7 shows an example of the disk 1 having a metallic hub. A disk 1 of this kind, on the surface of which a magnetic recording layer is formed, is accommodated in a hard case 2a to form a disk cartridge 2. A metallic hub 3 formed by a thin plate made of magnetic metal is secured to the central portion of the disk. An approximately quadratic chucking hole 4, in which the extremity portion of the spindle shaft is inserted, is formed in the central portion of this metallic hub 3 and an approximately rectangular positioning hole 5, in which the extremity portion of the driving pin is inserted to be engaged therewith, is formed in the peripheral portion. The disk cartridge 2 of this type is known generally as a 3.5 inch floppy disk cartridge.
Such a disk cartridge 2 rotates the disk 1 by chucking it by means of a disk chucking device of the disk driving device. In this disk chucking device, e.g. a rotating driving shaft, which is the driving shaft of a driving motor, is disposed at the center of the turn table so as to protrude therefrom and the driving pin is disposed, deviated from the center. Further, a yoke plate is mounted on the turn table through a bearing member of the rotating driving shaft and a magnet plate is secured to this yoke plate.
Now, the state, where the rotating driving shaft and the driving pin are engaged with the chucking hole 4 and the positioning hole 5 of the disk 1, respectively, will be explained. When the disk cartridge 2 is mounted on the turn table, the rotating driving shaft is engaged with the chucking hole 4. At this time, when the turn table is rotated, the driving pin is inserted in the positioning hole 5 to be engaged therewith. Then the driving pin is pushed by the front side of the positioning hole 5 in the rotational direction by the load torque applied to the disk 1. The driving pin is displaced in the direction, where it becomes gradually more distant from the rotating driving shaft of the turn table, while being moved backward in the rotational direction of the turn table against a spring and the driving pin is strongly pushed to the side of the positioning hole 5, which is closer to the periphery, by the displacement force. As the result, the metallic hub 3 is energized to be displaced in the direction where it becomes more distant from the rotating driving shaft of the turn table and the center of the disk 1 is positioned at the center of the turn table. In this way the metallic hub 3 is linked with the turn table in one body through the driving pin so that the disk 1 is driven so as to rotate together with the turn table.
However, in the device described above, since the driving pin is only pivoted around a fulcrum pin of a ring plate, if there are errors in the size between the chucking hole 4 and the positioning hole 5 disposed in the metallic hub 3 of the disk 1, the driving pin pushes no more a fixed position on the side of the positioning hole 5, which is closer to the periphery. Further deviations in the position, where the driving pin pushes the positioning hole 5, take place due to errors in the mounting of the driving pin or errors in the size of the ring plate. As the result, in the case where the index signal of the disk 1 is detected by detecting the rotational phase on the turn table side, positional deviations take place and therefore it is feared that the index cannot be detected precisely.
In order to solve the problem described above, a technique disclosed in JP-P-61-73263A has been proposed. This technique is shown in FIGS. 5 and 6.
As indicated in these figures, there are disposed a rotating driving shaft 6, which constitutes the output shaft of a driving motor not shown in the figure and at the same time the extremity of which is engaged with the central hole (chucking hole) formed in the central disk (metallic hub) secured to the center of the disk 1, and a driving pin 7, which is engaged with a driving pin engaging hole (positioning hole) formed at a position deviated from the center of the central disk 3.
A rotor 9, on the inner peripheral surface of which a ring-shaped magnet 8 constituting the driving motor is mounted, is mounted on the rotating driving shaft 6 described above through a bearing member 10. A ring plate 11 is mounted on the extremity side of the rotating driving shaft 6 through the bearing member 10 described above, located on the rotor 9. Similarly a rotating lever mounting plate 12 is mounted on this ring plate 11 through the bearing member 10. Further a magnet plate 13 attracting the central disk 3 of the disk 1 is secured to this rotating lever mounting plate 12.
Furthermore a rotating lever 14 formed in an approximately semicircular shape, curved so as to surround the outer periphery of the rotating driving shaft 6, is mounted between the ring plate 11 and the rotating lever mounting plate 12. The driving pin 7 is planted on one end of this rotating lever 14 and an elongated hole 15, whose major diameter is in the radial direction, is formed on the base end side thereof. On the other hand, a pivot pin 18 is planted on the lower surface of the rotating lever mounting plate 12, which pin 18 is inserted in through holes 16 and 17 formed in the ring plate 11 and the rotor 9, respectively, and the extremity of which pin protrudes from the lower surface of the rotor 9. The rotating lever 14 is mounted by inserting the pivot pin 18 in the elongated hole 15 described above so that it is freely supported by this pivot pin 18 and by engaging the driving pin 7 on the extremity side with the positioning hole 19 formed in the rotating lever mounting plate 12 so as to protrude therefrom. This positioning hole 19 is formed in an approximately sector shape so as to be narrower on the inner periphery side. Further a coil spring 20 serving as energizing means is extended between an engaging piece disposed on the base end edge so as to protrude therefrom and another engaging piece standing on the middle portion of the rotating lever mounting plate. The rotating lever 14 described above is energized so as to rotate in the direction indicated by an arrow A in FIG. 6 and pushes the driving pin 7 to one side 19a of the positioning hole 19, which is the front side in the rotational direction of the rotor 9. In this way, since the rotating lever 14 is energized to be rotated and the driving pin 7 is pushed to one side of the positioning pin 19, the positioning of the driving pin 7 is effected.
In such a prior art example, when there are errors in the size between the central hole 4 in the central disk 3 of the disk 1 and the driving pin engaging hole 5, and the disk 1 is positioned, while pushing two sides of the central hole 4 to the side surface of the rotating driving shaft 6, in the case where the driving pin 7 is not positioned at the corner portion formed by the side, which is on the outer periphery side, and the front side in the rotational direction, but it is engaged with the middle portion of the side, which is on the outer periphery side, the position of the pivot pin 18 is varied by moving appropriately the rotating lever in an extent of the elongated hole 15. Then, the driving pin 7 is moved within the driving pin engaging hole 5 so that the engaging position of the driving pin 5 with the driving pin engaging hole 15 is kept always constant.
Now, according to the prior art technique described above, the elongated hole 15 formed in the rotating lever 14 is freely supported on the mounting plate by the pivot pin 18 and the position of the pivot pin 18 is varied by moving appropriately the rotating lever 14 in the extent of the elongated hole 15.
However, at this varying operation, since the pivot pin 18 is slid on the contour of the elongated hole 15 while being thrust thereto by a coil spring 20, torque loss is produced. In addition, since loss was great, if burrs remained after cutting, fabrication cost was increased. Further, it was feared that disarrangements in the size are produced because of wear by sliding and that powder produced by wear has bad influences on the recording/writing of recorded data.